Description
Specimens of this species reach about 10 mm in length. Almost the entire body is translucent with a pink hue. The dorsum is crossed by a white longitudinal line that reaches the end of the tail from the head. In front of the rhinophores there are often some small irregular white spots, which may also form a discontinuous line on both sides of the body, right below the insertion of the rhinophores. Oral palps are long and pink, with a white-pigmented tip. The rhinophores are also pink and have white tips, having about 8-10 lamellae in adults, although juveniles may lack them. There are 4-5 groups of cerata that remain fairly close together, almost without apparent separation but between the first and second group, where the peculiar genital papilla is located. The first two groups of cerata have 4-5 rows. The digestive gland inside the cerata is brown and the anterior surface of the cerata is white. Between the first and second group of cerata, on the right side, there is a curious structure that Vayssière, in his original description of 1888, already understood it was some kind of genital structure: it is the penial sheet, coloured pink, wide and festooned, with two digitations at their tips. The foot, also coloured pink, widens towards the front end, but without forming labial palps.

Biology
Although this is a species that is not a rare finding in well-lit rock surfaces with abundant algae, its biology and eating habits are almost unknown. It presumably feeds on hydrozoans as the other species of Facelinidae. Due to the shape of the penial sheet, observation of the reproductive behaviour of two individuals can be very interesting.

Etymology

Facelina: means “lined face”.

“-opsis“: is a suffix referred to “small” or “tiny”. In this case Facelinopsis means “small Facelina” o “small lined face”, but we must state that , according to Perrier, suffix “-opsis” implies “similar to”.

Distribution
This is a species whose distribution is limited to the western Mediterranean, having been cited in the coasts of Corsica and, in the Iberian Peninsula, in the Huelva coast, in the Strait of Gibraltar, on the Mediterranean coast of Andalusia and Catalonia (Costa Brava).